The present invention relates to a silver halide photographic light-sensitive material and more particularly to a silver halide photographic light-sensitive material which is high in sensitivity and contrast and less in fogging for high intensity exposure to red light and is excellent in time stability of the emulsion.
With recent rapid progress of information transmission systems, the silver halide photographic light-sensitive materials are increasingly required to have the higher sensitivity. Examples of these systems are high-speed photo-composing system in which the information which is output from electronic computers is rapidly displayed as letters or figures by cathode-ray tubes and press facsimiles for rapid transmission of press manuscripts to remote places.
The characteristics required for the silver halide photographic light-sensitive materials used for such systems are high sensitivity, high contrast and high resolving power for so-called high-intensity and short-time exposure, namely, exposure for a short time of 10.sup.-4 second or less with a light source such as cathode ray tube (CRT), a gas laser such as argon or helium-neon or light emitting diode (LED). Among these light sources, the scanner system of argon laser has conventionally been mainly employed. This system can provide high output, but the apparatus is large-sized and expensive. Therefore, recently, apparatuses having the compact and inexpensive helium-neon laser or LED as the light source are sold from many companies and silver halide photographic light-sensitive materials high in sensitivity for these light sources are desired.
It is known to use trinuclear cyanines as sensitizing dyes in the case of exposure to such light sources of red light. These cyanines have a spectral absorption maximum in the region of about 600-680 nm and are very effective for sensitization to red light of helium-neon laser or LED. However, they tend to increase fog formation when added in a large amount. Use of antifoggants for inhibition of formation of fog causes deterioration in developability or reduction in sensitivity due to desorption of the dyes. If chemical sensitization is diminished, the sensitivity is insufficient and if the addition amount of the dye is increased, occurrence of fog further increases and retention of color of the dye increases to deteriorate the quality of images. Accordingly, there have been desired light-sensitive materials which are less in remaining of color of the dye, less in fogging and besides, high in sensitivity and contrast even when subjected to high-intensity exposure.
It is also known to add a water-soluble rhodium compound for preparing a high contrast silver halide photographic emulsion. However, when a silver halide emulsion prepared with addition of the said sensitizing dye and the rhodium compound in combination is coated on a photographic support, the sensitivity of the emulsion sometimes changes during the period of from the finishing of the emulsion until the coating of the emulsion or during the coating of the emulsion. Thus, there have been problems in stability in preparation of the emulsion and stability in quality of light-sensitive materials.
Consumption of silver halide photographic light-sensitive materials is increasing steadily and in many cases, the light-sensitive materials are processed in a short time at a high temperature for increasing the processing amount of the materials. Therefore, demand has more and more increased for light-sensitive materials which are high in sensitivity and less in formation of fog even when processed in a short time and at a high temperature and can give a certain photographic characteristics even if the processing conditions are somewhat deflected.
Silver iodobromide emulsions sensitized with gold and sulfur are widely known as emulsions having high sensitivity to high-intensity exposure. However, the light-sensitive materials coated with such emulsions sometimes show delay in developability or inferior clearing in fixation because of the short time development in processing of the film materials of a relatively large silver halide amount. Thus, demand for stability in processing of light-sensitive materials has further been increased.